Water soluble polymer additives for polyurethane-based pressure sensitive adhesives

ABSTRACT

In accordance with the present invention novel polyurethane PSAs containing water soluble polymer additives have enhanced water uptake. The water soluble polymer additives suitable for use herein have a solubility parameter in poorly hydrogen-binding solvents (e.g., hexane, cyclohexane and the like) in the range of from 8-10. The water soluble polymers must also be free from moieties which will react with isocyanates. Such PSAs retain their transparency and peel strength characteristics and can still be employed as relatively thin films (i.e., 2 to 100 mils) while exhibiting only minimal swelling when in contact with moist environments.

This invention relates to polyurethane-based pressure sensitiveadhesives ("PSAs") including certain water soluble polymer additives toenhance water uptake, and is more particularly concerned with medicalproducts utilizing such PSAs wherein the properties of the adhesive isnot adversely affected by the polymer additives.

BACKGROUND OF THE INVENTION

Until the early 1950's commonly used pressure sensitive adhesives("PSAs") for skin applications were based on natural or synthetic rubbercompositions compounded with low molecular weight tackifiers,plasticizers, stabilizers, etc. These adhesives had the disadvantage ofbeing quite hydrophobic and incapable of absorbing water. Thus, suchadhesives would trap water under the covered area, often causing skinmaceration or other skin damage. Furthermore, the low molecular weightingredients compounded into these adhesives often would penetrate theskin, causing irritation or sensitization.

Polyacrylate PSAs are an improvement over the rubber-based adhesives,partly due to their self-adhesive property. This property allows them tobe prepared as single-component polymeric materials without the need forpotentially allergenic modifying or tackifying agents. However, theseadhesives often contain unreacted residual acrylic monomer as animpurity in an amount which would irritate and/or sensitize skin.Although these polyacrylate PSAs are much more permeable to moisture orwater vapor than are the rubber-based adhesives, they are incapable ofabsorbing any significant amounts of moisture or water. Therefore, whenused for long duration in skin or wound care applications, adhesion iscompromised and/or skin damage or maceration may result.

One variation of these polyacrylate PSAs is disclosed in U.S. Pat. No.4,914,173 to Ansell. The specific PSAs of that patent are obtained byreacting an isocyanate prepolymer, which is the reaction product of apoly-functional isocyanate and a polyoxyalkylene diol monoalkyl ether,with a hydroxy-containing ester of acrylic or methacrylic acid to form apolymer and then cross-linking the polymer by irradiation to form a PSAthat is not self-adherent but is capable of absorbing up to 95% byweight of water when hydrated. Although useful in applications where theadhesive will contact a moist or wet environment, these adhesives do nothave sufficient tack or initial adhesive properties to be adherent tothe skin for certain uses.

An advance in PSA formulation for skin and particularly for wound careapplications was the development of compositions comprising blends ofone or more water-soluble or swellable hydrocolloids and a tacky,viscous, polymeric material such as polyisobutylene as disclosed in ChenU.S. Pat. No. 3,339,546. Another example is Doyle et al., U.S. Pat. No.4,551,490, which discloses medicinal grade pressure sensitivecompositions containing polyisobutylenes or blends of polyisobutylenesand butyl rubber, a styrenic radical or block type copolymer, mineraloil and water soluble hydrocolloid gum and a tackifier. Suchhydrocolloid containing PSAs have the advantage of providing the desiredadhesion to skin and, at the same time, are capable of absorbingtransepidermal water loss (i.e., perspiration) or other body fluids,including wound exudates.

Hydrocolloid containing PSAs have found use in medical applications suchas ostomy devices and wound dressings, where the adhesives maintain thedevice on skin for several days without skin damage. However, existinghydrocolloid PSAs have substantial limitations in that they are opaque,lack quick initial tack, and tend to disintegrate upon excessive waterabsorption.

Polyurethanes are polymeric products of diols or polyols anddiisocyanates or polyisocyanates. Despite the broad applications ofpolyurethane chemistry, polyurethane based PSAs are not widely used andto date have been found suitable for only a few specializedapplications. A suitable balance of elastic and viscous properties whichis required in a PSA has not been readily attainable in conventionalpolyurethane materials.

Existing polyurethane based adhesives function either as weak elasticsor simply as high viscosity liquids. The adhesives composed of theelastic type polyurethanes tend to fail by gradually peeling away fromsurfaces to which they have been applied. The high viscosity typepolyurethanes, which are typically obtained by using a substantialexcess of polyol, leave a residue upon removal, and their cohesivestrength is too low to withstand the stresses applied in manyapplications.

The difficulty of attaining this balance of viscoelastic characteristicsin a polyurethane explains the paucity of prior art polyurethane PSAliterature. Allen et al., U.S. Pat. No. 4,497,914, discloses an ostomygasket adhesive comprised of a polyurethane prepared by reaction of anorganic polyisocyanate with one or more di or polyfunctional hydroxylcompounds, for example, polyols derived from propylene or ethyleneoxide, in which is incorporated a hydrophilic filler, such as acellulosic or natural gum. The adhesive is capable of absorbing bodilyfluids by virtue of dispersed hydrophilic filler physically encapsulatedwithin the self-sustaining polyurethane adhesive composition.

Muller et al. U.S. Pat. No. 3,930,102 discloses the preparation of awebstock having a self-adhesive polyurethane coating produced by thereaction of a trifunctional propylene oxide based polyol and analiphatic diisocyanate employing an NCO/OH ratio in the range of 0.71 to0.85. This type of webstock is said to be suitable for the production oflabels and tapes. However, these compositions are not sufficientlyhydrophilic to allow absorption of bodily fluids.

A need thus exists for polyurethane pressure sensitive adhesives forskin application which have adequate moisture absorption or permeationcapacities and have other desired properties, such as transparency,conformability to body shape, quick tack, adhesive strength tailorableto the application, high wet strength, and lack of cold flow.

Copending application U.S. Ser. No. 973,448, entitled "PolyurethanePressure Sensitive Adhesives," filed Nov. 9, 1992, issued as U.S. Pat.No. 5,591,820 discloses a novel class of polyurethane-based pressuresensitive adhesives (PSAs) which exhibit a high degree of waterabsorption and/or water vapor transmission capabilities. Specifically,these PSAs comprise a polyurethane polymer having excess hydroxylfunctionality, a glass transition temperature of less than about 0° C.,a moisture absorption at equilibrium of at least about 70% of its weightand/or a moisture vapor transmission rate of at least about 300grams/meter² /24 hours at 37° C. and 90% relative humidity. Theseproperties provide that such PSAs are ideally suited for medical usesincluding, but not limited to, ostomy devices, wound dressings, and thelike. In addition to these desirable hydrophilic and vapor transmissionqualities, the above polyurethane based adhesives have good peelstrength and provide a desirable thin, transparent adhesive film.

Incorporation of hydrocolloids, or water soluble polymers (hereinafter"water soluble polymers"), into such adhesives to enhance moistureuptake has been previously found to sacrifice the desirablecharacteristics of the polyurethane-based PSAs. For example,incorporation of sodium carboxymethylcellulose or pectin renders thefilms opaque and may result in a substantial degree of swelling in moistenvironments.

Additives for use in polyurethane-based PSAs which will enhance wateruptake without adversely affecting the PSA would be a useful addition tothe art.

SUMMARY OF THE INVENTION

In accordance with the present invention novel polyurethane PSAscontaining water soluble polymer additives have enhanced water uptake.The water soluble polymer additives suitable for use herein have asolubility parameter in poorly hydrogen-binding solvents (e.g., hexane,cyclohexane and the like) in the range of from 8-10. The water solublepolymers must also be free from moieties which will react withisocyanates. Such PSAs retain their transparency and peel strengthcharacteristics and can still be employed as relatively thin films(i.e., 2 to 100 mils) while exhibiting only minimal swelling when incontact with moist environments.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front view of an ostomy gasket which includes a PSA band inaccordance with the invention.

FIG. 2 is a rear view of the gasket of FIG. 1.

FIG. 3 is an enlarged cross-sectional view of the gasket of FIGS. 1 and2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has now been found that the class of water soluble polymers having asolubility constant in the range of from 8 to 10 and free from moietieswhich will react with isocyanate groups are excellent additives topolyurethane PSAs, in that the integrity and desirable characteristicsof the PSA film are maintained while providing enhanced water uptake.This class of water soluble polymers is chosen so as to be substantiallymiscible in both the polyol and isocyanate components which are used toprepare the polyurethane PSA. Indeed, the preparation of the presentPSAs involves, inter alia, dissolving a desired water soluble polymer ineither the polyol or isocyanate component and thereafter reacting thecomponents to form the corresponding polyurethane PSA. For example, thewater soluble polymer is preferably dissolved into a polyol solutioncontaining a catalyst prior to reaction with the isocyanates.Thereafter, the so-formed premixture is reacted with isocyanates,preferably in an NCO/OH mole weight ratio of from about 0.5/1 to about0.99/1 to provide a clear adhesive.

Typical water soluble polymers having a solubility constant in the rangeof from 8 to 10 include poly(2-ethyl-2-oxazoline),poly(vinylmethylether) and the like. Most preferred ispoly(vinylmethylether) commercially available from BASF as Lutonal M-40.In accordance with this invention, the water soluble polymers can beadded to the polyurethane PSA in amounts corresponding to the degree ofwater uptake desired in the final product. Typically the polymers arepresent in a range of from about 1 to about 40% by weight of the PSAformulation. Preferred adhesives contain about 25 to 35% by weight ofthe water soluble polymer and most preferred adhesives contain about 30%by weight.

The water soluble polymer additives having a solubility constant in therange of from 8 to 10 can be added to any polyurethane-based PSA toenhance water uptake. These additives are ideally suited forincorporation into the polyurethane adhesives disclosed in copendingU.S. Ser. No. 973,448, issued as U.S. Pat. No. 5,591,820, mentionedabove.

Thus, preferably the pressure-sensitive adhesives comprise apolyurethane polymer having excess hydroxyl functionality, a glasstransition temperature of less than about 0° C., a moisture absorptionat equilibrium of at least about 20% of its weight and/or a moisturevapor transmission rate of at least about 300 grams/meter² /24 hoursmeasured at 37° C. and a 90% relative humidity gradient. Advantageously,the glass transition temperature of the polymer is less than about -30°C., the moisture absorption at equilibrium of at least about 100% of itsweight and/or the moisture vapor transmission rate is at least about 500grams/meter² /24 hours. These polymers provide a peel adhesion to humanskin of between about 0.3 and 4 and preferably between about 0.5 and 3.5newtons/cm width of the polymer.

Preferably, the polyurethane polymer is formed by the reaction of anisocyanate component and a polyol component at a molar ratio ofisocyanate moieties to hydroxyl moieties of less than one with at leastone of the components having a functionality that is greater than two tofacilitate crosslinking. The polymer is crosslinked to a crosslinkdensity alpha (α) defined by the equation ##EQU1## wherein i=1 to nwhere n is the number of the reactant components

X_(i) =mole fraction of i_(th) component

F_(i) =functionality of the i_(th) component

r=the NCO/OH molar ratio

Mw=Molecular weight of the polyol

of between about 10⁻⁴ and 10⁻³ to obtain the desired properties. Whenthe isocyanate component is an aliphatic polyisocyanate, the crosslinkdensity is preferably between about 2×10⁻⁴ and 10⁻³, while for aromaticpolyisocyanates the crosslink density is preferably between about 4×10⁻⁴and 9×10⁻⁴.

A preferred molar ratio is between about 0.5 and 0.99, and morepreferably between about 0.65 and 0.99, and most preferably betweenabout 0.85 and 0.99. The polyol component advantageously comprises apolyether polyol having a molecular weight of between about 1000 and10,000, such as a homopolymer or copolymer containing ethylene oxide orpropylene oxide groups. The polyol component may also be a hydroxylterminated prepolymer. When moisture absorbent adhesives are desired,the polyol component can be a polyether diol or triol containing atleast about 30% by weight or ethylene oxide groups.

The isocyanate component has a functionality of equal to or greater than2, and may be an aliphatic polyisocyanate, an aromatic polyisocyanate orcombinations thereof. Also, the isocyanate component may be anisocyanate terminated prepolymer. As noted, at least one of theisocyanate or polyol components must have a functionality of greaterthan 2 to obtain the desired crosslinking of the polymer.

The invention also relates to a medical article or device forapplication to skin which comprises a layer of the pressure-sensitiveadhesive described above and a backing material in contact with at leasta portion of one side of the layer. The backing material in contact withat least a portion of one side of the layer. The backing material may bea natural or synthetic fiber, a woven or non-woven fabric, paper or athermoplastic polymer. Also, a release layer in contact with the side ofthe pressure-sensitive adhesive layer in contact with the side of thepressure-sensitive adhesive layer opposite the backing material may beincluded to protect the adhesive prior to use. Thus, the release layercomprises a material that does not permanently bond to thepressure-sensitive adhesive layer, such as a silicone coating.

This medical article may also include a backing layer and a layer of thepressure sensitive adhesive described above on at least a portion of oneside of the backing layer for contacting the skin and securing thearticle thereto. This article advantageously includes a moisture orwater absorbent material positioned for placement upon a moist or wetenvironment, wherein the pressure sensitive adhesive layer is locatedadjacent at least a portion of the absorbent material. If the absorbentmaterial is in the form of a disk, the pressure sensitive material layermay be associated with and at least partially surround the perimeter ofthe disk. A support layer may be provided for the absorbent materialsuch that the pressure-sensitive adhesive layer is attached onto atleast a portion of the periphery of the support layer and surrounds theentire perimeter of the disk.

In another embodiment, the medical article further comprises anattachment member for connection to another medical device, such as abag or container. Thus, the disk would include an aperture therein topermit passage of a fluid therethrough. To provide a secure attachmentto the patient and to prevent leakage, means for joining thepressure-sensitive adhesive layer to the support layer may be used, suchas an ultrasonic weld.

Accordingly, the medical article or device of the invention may beprovided in the form of an ostomy device, a wound dressing, a medicaltape, a bandage, an incontinence device, a dermatological device, atransdermal device, a surgical incise drape or an intravenous cathetersecurement device.

Another embodiment of the invention relates to a method for making apressure-sensitive adhesive for application to skin which comprisespremixing the desired water soluble polymer into either the isocyanatecomponent or the polyol component and then providing a mixture of theisocyanate component and the polyol component at a molar ratio ofisocyanate moieties to hydroxyl moieties of less than one; selecting atleast one of the components to have a functionality that is greater thantwo to facilitate crosslinking and reacting the isocyanate and polyolcomponents in the presence of a catalyst to form a polyurethane polymerhaving a glass transition temperature of less than about 0° C., amoisture absorption at equilibrium of at least about 20% of its weightand/or a vapor transmission rate of at least about 300 grams/meter² /24hours measured at 17° C. and a 90% relative humidity gradient.

The mixture may be cast upon a substrate and heated at a sufficienttemperature of between about 100° and 150° C. and for a sufficient timeof between about 1 to 25 minutes to form a layer of the polymer. Thislayer may be provided upon a backing material or a release layer andwould possess a peel adhesion to human skin of between about 0.3 and 4and preferably between about 0.5 and 3.5 newtons/cm width of thepolymer.

Preferably, a polyol component is a polyol having a molecular weight offrom about 1,000 to about 10,000 or mixtures of such polyols, with anisocyanate such as a polyisocyanate. Although any of a wide variety ofpolyols can be used, those which are not crystalline are the mostsuitable. Exemplary polyols include polyether diols or triols (ethyleneoxide and propylene oxide polymers and copolymers) such as thoseavailable from Olin (e.g., the Poly G series). In general, forcomparable formulations, the higher molecular weight polyols wouldprovide greater peel strengths in the resulting adhesive.

Where increased moisture or water absorption properties are desired inthe PSA, polyols that contain a significant amount of polyoxyethyleneare used so as to increase the hydrophilic character of the polymer.These polyols should contain at least about 30% of polyoxyethylene inorder to enable the polymer to absorb water in an amount of at leastabout 20% of its weight and as high as 400 to 1000%.

Typical polyols which are useful for this embodiment include DowChemical's XUS15176 and the various commercial Carbowaxes which areavailable in a range of molecular weights from the Union CarbideCorporation. Representative Carbowaxes are PEG (Carbowa 1450) and PEG(Carbowax 8000) in which the numbers refer to molecular weights. Theproportion of polyoxyethylene which is present in the polyol willdetermine the degree of hydrophilic character of the polyurethane.Increasing the amount of polyoxyethylene promotes strong hydrophilicproperties to the final product, while a lessened hydrophilic characterresults by increasing the proportion of polyoxypropylene in the polyol.

The functionality of the polyol that is used is at least 2 and usuallyis greater than 2, with the higher functionalities providing increasedcrosslinking of the polyurethane. A number of polyols which are suitablewhen used alone or in combination are listed below in Table 1.

The isocyanates which may be used in making the polyurethanes of thePSAs of the invention may be represented by R(NCO)n wherein n is atlevel 2 and preferably between about 2 and 4, and R is an aliphatic,alicyclic, aliphatic-alicyclic, aromatic, or aliphatic-aromatichydrocarbon compound ranging from about 4 to 26 carbon atoms, but moreconventionally from about 6 to 20 and generally from about 6 to 13carbon atoms.

                  TABLE 1                                                         ______________________________________                                        SUITABLE POLYOLS                                                              Component  Functionality                                                                            Equivalent                                                                             ETO %  Supplier                                ______________________________________                                        POLY G                                                                        55-28      2          2025.00  30     OLJN                                    55-37      2          1512.00  30     OLJN                                    55-56      2          976.00   45     OLJN                                    76-120     3          457.00   30     OLJN                                    83-34      3          1576.00  70     OLJN                                    85-28      3          2025.00  10     OLJN                                    85-36      3          1508.00  17     OLJN                                    Voranol                                                                       5148       3          2357.00  19     DOW                                     5287       2          1018.00  12     DOW                                     5471       3          1603.00  14     DOW                                     Voran                                                                         220-037    2          1500.00  0      DOW                                     232-034    3          1636.00  14     DOW                                     240-446    4.5        125.10   0      DOW                                     240-800    4          69.70    0      DOW                                     270-370    7          155.90   0      DOW                                     XUS 15176.00                                                                             2          1500.00  30     DOW                                     Multranol 3400                                                                           3          1000.00  0      MOBAY                                   Multranol 3901                                                                           3          1997.00  0      MOBAY                                   Multranol 9133                                                                           3          53.95    0      MOBAY                                   Desmofen 2500                                                                            2          505.00   0      MOBAY                                   Quadrol    4          73.00    0      MOBAY                                   Carbowax                                                                      1450       2          714.00   100    CARBIDE                                 3350       2          1638.00  100    CARBIDE                                 4600       2          2352.00  100    CARBIDE                                 8000       2          4141.00  100    CARBIDE                                 Terathane                                                                     1000       2          500.00   0      DUPONT                                  2000       2          1024.00  0      DUPONT                                  Pluracol 380                                                                             3          2235.00  0      BASF                                    Poly THF ER 1250                                                                         2          625.00   0      BASF                                    Fomrez                                                                        EPD-56     2          1041.00  45     WITCO                                   EPD-28     2          2086.00  45     WITCO                                   K22-170    6          308.00   90     WITCO                                   L49-28     3          1990.00  25     WITCO                                   ECFL1000Y  3          278.00   90     WITCO                                   Witcon1 Peg1000L                                                                         2          505.00   90     WITCO                                   ______________________________________                                    

Representative examples of diisocyanates include aliphatic isocyanatessuch as tetramethylene diisocyanate, hexamethylene diisocyanate,trimethylhexamethylene diisocyanate, dimer acid diisocyanate, isophoronediisocyanate, diethylbenzene diisocyanate, decamethylene1,10-diisocyanate, cyclohexylene 1,2-diisocyanate andcylohexylene-1,4-diisocyanate and the aromatic isocyanates such as 2,4and 2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate,1,4-naphthalene diisocyanate, dianisidine diisocyanate, toluidinediisocyanate, m-xylylene, diisocyanatetetrahydronaphthalene-1,5-diisocyanate, andbis(4-isocyanatophenyl)methane.

Polymeric polyisocyanates having a functionality of greater than 2, suchas neopentyl tetraisocyanate, can also be used. A number of suitableisocyanates are listed in Table 2 below. In addition, mixtures of di-and tri-functional isocyanates are commercially available and may beused to obtain an isocyanate component having a functionality of between2 and 3, while mixtures of tri- and tetra-functional isocyanates may beused to obtain functionalities of between 3 and 4 (i.e., DESMODUR N 3300from Miles, Perkasie, Pa.). These tri- and tetra-functional isocyanatesare illustrated below.

                  TABLE 2                                                         ______________________________________                                        SUITABLE ISOCYANATES                                                          Component   Functionality                                                                             Equivalent                                                                             Supplier                                     ______________________________________                                        PAPI 94     2.2         131.50   DOW                                          PAPI 2580   3           139.60   DOW                                          ISONATE 2181                                                                              2           182.60   DOW                                          ISONATE 2125m                                                                             2           125.50   DOW                                          MONDUR MR   2.7         131.00   MOBAY                                        MONDUR CD   2           143.00   MOBAY                                        MONDUR CB75 3           323.00   MOBAY                                        DESMODUR W  2           132.00   MOBAY                                        TMXDI       2           122.10   CYANAMID                                     CYTHANE 3160                                                                              3           404.00   CYANAMID                                     TDI 80      2           87.00    OLJN                                         DMI 1410    2           295.77   HENKEL                                       ______________________________________                                    

Desmodur N 3300 has a functionality of about 3.4-3.6 and it is a mixtureof the two isocyanates depicted above. This isocyanate compound ispreferred from the standpoint of toxicity because it is an aliphaticisocyanate derivative that produces a non-toxic degradation product.Furthermore, the isocyanate compounds shown above can be mixed togetheror with the diisocyanates mentioned above to attain the desiredfunctionality of the isocyanate component.

Generally speaking, the polyurethane is prepared from about 75% to 95%of the polyol, and about 5% to 25% of the polyisocyanate. The relativeamounts are selected so that the NCO/OH ratio is between about 0.5 and0.99 and preferably between about 0.65 to 0.99, so that thesepolyurethanes have excess hydroxyl functionality.

In preparing the polyether polyurethane adhesives of this invention, thepolyols and the polyisocyanates are reacted in the presence of knowncatalysts for such reaction, for example, tin salts and organic tinesters such as dibutyltin dilaunate and stannous octoate. Anadvantageous catalyst is METACURE T-12 by Air Products and Chemicals,Inc., because this catalyst has been approved by the FDA for medicalapplication and provides a satisfactory reaction.

Also, it is preferred for the pressure-sensitive adhesive to have aglass transition temperature (Tg) of less than 0° C. and preferably lessthan -30° C. Thus, the amount of crystalline polyol used, if any, shouldbe held to a minimum. By choosing polyols which are not crystalline ordo not crystallize, or which do not cause phase separation duringreaction, a transparent, uncolored polymer is obtained. A coloredpolymer is also avoided by selecting isocyanate and polyol componentswhich form polymerization products that do not contain multiple bondswhich would be capable of absorbing light or heat energy and undergotransformations resulting in colors.

The pressure-sensitive polyurethane adhesives of this invention eachhave an MVTR (at equilibrium) of at least 300 and preferably greaterthan 500 g/m² /day when measured at 37° C. and a 90% relative humiditygradient. When these adhesives are applied onto skin, the skin can"breathe," such that any excess moisture generated by perspiration ofthe skin can pass through the adhesive to prevent deterioration of theskin, while some moisture is retained to provide an environment whichpromotes healing.

In copending application U.S. Ser. No. 973,448, entitled "PolyurethanePressure Sensitive Adhesives" filed Nov. 9, 1992, issued as U.S. Pat.No. 5,591,820, it has been disclosed that the polyurethane adhesive peelstrength, for a given backing and at a given adhesive thickness, is afunction of the extent of crosslinking which, in turn, depends upon thefunctionality of the components used to form the polyurethane polymer.The extent of crosslinking can be expressed as the number of crosslinksper unit weight. With a greater extent of crosslinking, the peeladhesion becomes lower, such that peel adhesion has been found to beinversely related to the extent of crosslinking.

It was further found that this crosslink density is a function of aninterplay of molecular parameters of the polyurethane components. Amathematical relationship incorporating these components has beenderived to define the optimum combination of the kind and proportions ofthe components which results in the formation of polyurethane PSAs forthe specified medical uses. This relationship can be used to calculate avalue, designated as α, which is representative of the extent ofcrosslinking of the polymer. Thus, the α value, which is based on theaverage functionality of the reactants, the NCO/OH mole ratio, and themolecular weight of the polyol, may be used as a measure of theperformance of one polymer relative to another, as well as to selectwhich polymers are useful in accordance with the teachings of thepresent invention.

The following expression sets forth the relationship between thevariables which is used to calculate α. As noted above, the peelstrength is inversely proportional to the extent of crosslinking whichcan be expressed as follows: ##EQU2## wherein the number ofcrosslinks/units weight of polymer is proportional to α as calculated bythe following formula: ##EQU3## wherein i=1 to n where n is the numberof the reactant components

X_(i) =mole fraction of i_(th) component

F_(i) =functionality of the i_(th) component

r=the NCO/OH molar ratio

Mw=Molecular weight of the polyol.

Thus, in a given polyurethane formulation, an interplay of differentparameters governs the peel strength of the adhesive.

An α value in the range of 10⁻⁴ to 10⁻³ is representative of an adhesivewhich has the desired balance of cohesive and adhesive characteristicswhich are typically required for a pressure-sensitive adhesive, with αvalues of between 2×10⁻⁴ and 10⁻³ for aliphatic polyurethanes andbetween 4 and 9×10⁻⁴ for aromatic polyurethanes being particularlyadvantageous.

Accordingly, based upon this information, one skilled in the art canroutinely select the particular isocyanate and polyol components andmolar ratios thereof to obtain polyurethane polymers which have α valueswhich fall in the desired ranges. In addition, the α value can becalculated prior to actual formulation of the polymer, so that theexperimental work is necessary only after selecting those components andmolar ratios which provide α values in the desired range.

The pressure-sensitive adhesive products of this invention are preparedby coating a mixture of the polyurethane adhesive components on abacking material and allowing the polyurethane components to cure.Useful backing materials are thermoplastic elastomers such aspolyurethane film, plasticized PVC, breathable woven or non-wovenfabrics made of natural or synthetic fibers such as polyester and porouspaper. The adhesive components can also be applied to a release linersuch as mylar film with a silicone coating and silicone coated paper andthen after curing removed and placed on a backing material. Thethickness of the adhesive coating is about 1 to 60 mils depending uponthe requirements of the specific product application, while the backingmaterial has a thickness in the range of between about 0.5 and 5 milsand typically about 1-2 mils.

The above-described polyurethane pressure-sensitive adhesives areparticularly useful for attaching medical devices and other materials tothe skin. The adhesives can be used as or applied to bandages, ostomydevices, incontinence devices, incise drapes, intravenous catheterholders, transdermal drug delivery devices and medical tapes such aswound closure tapes. Where absorbent adhesives are desired, such as inwound dressings, the polymers that have high water absorption propertiescan be successfully used. Because of the skin adhesion properties ofthese PSAs, i.e., no skin irritation or sensitization, and lack of skinor hair adhesion on removal, these adhesives are skin friendly and arevery useful in the medical field where skin contact is required.

FIGS. 1-3 illustrate an ostomy gasket 10 which includes adhesives madeof the polymers of the present invention. This device has a centralaperture 15 for placement over the incision and through which fluids maydrain. Adjacent to and surrounding the aperture 15 is a layer 20 of anadhesive material which has highly absorbent properties to withstand themoist environment and fluids which drain through the aperture. Thislayer 20 is preferably made of material such as STOMAHESIVE, which isavailable from ConvaTec, Skillman, N.J. Alternatively, this layer 20 ofabsorbent material can be of a pressure-sensitive adhesive in accordancewith the invention which includes a high ethylene oxide content.

This absorbent material 20 is preferably supported on a polyethylenefilm 25. When an adhesive material such as STOMAHESIVE or the like isused, the opposite side (or working face) of this layer 20 includesrelease liner 30 which allows handling of the article without concern asto the absorbent material adhering to unintended surfaces.

The polyethylene film support 25 is secured to a flange 35 which isadapted to receive an ostomy bottle or other container for storing thefluid which passes through aperture 15. Thus, flange 35 includes a lip40 and corresponding recess 45 to facilitate attachment of the bottle orcontainer thereto. Flange 35 is attached to disk shaped extension 50. Asupportive adhesive band 55 in accordance with the invention completelysurrounds the periphery of the flange 35. This band 55 includes apolyester fiber backing layer 60 upon which is placed an adhesive of thepresent application. This adhesive is shown as 65. To prevent theadhesive from sticking to surfaces prior to the desired time of use, arelease layer 70 is provided on the side opposite the backing layer(i.e., the adhesive face). As shown in FIG. 2, the backing layerincludes cut notches 75 to facilitate removing a portion of the backing80 and thus more easily expose the adhesive face for attachment to thedesired surfaces.

Adhesive band 55 is attached to the top of flange extension 50 andadhered thereto due to the adhesive properties of layer 65. To obtain amore secure connection between band 55 and flange portion 50, a plasticring 85 is placed upon the backing member 60 of the band 55 and isultrasonically welded to extension 50 of flange 35.

When the device is to be used, the release layers 70 and 30 are firstremoved thus exposing the PSA material 65 of band 55 and the absorbentmaterial 20. The PSA material 65 as noted above is skin friendly andprovides a secure bond to the skin without damaging it. Thus, the gasketis retained in the desired place despite whether absorbent layer 20 hasadhesive characteristics or not. When absorbent layer 20 is made of ahighly water absorbent material, it most often does not developsufficient tack or peel strength so that it can be properly secured inplace on the patient. Thus, the PSA adhesive 65 provides a securebonding of the gasket to the patient and holds the absorbent layer inplace so that any further bonding due to the adhesive properties ofabsorbent 20 can occur over time. Again, as noted above, PSA layer 65allows the skin to breathe so that excessive fluid does not accumulatethereon and cause damage or other detrimental affects to the skin.

The following examples, which are intended to illustrate the inventiondescribed herein without unduly restricting it, provide furtherillustrations of how to select the appropriate components and amountsthereof to form the desired pressure-sensitive adhesives.

EXAMPLE 1 Hydrophobic Polyurethane Adhesive With 29% Loading ofPolyvinyl Methyl Ether (Lutonal M40)

A homogeneous polyol-Lutonal M40 solution was prepared by dissolving28.8 parts of polyvinyl methyl ether (Lutonal M40 from BASF) in a 64.5parts of heated (80° C.) polyol (Poly G 26-37 from Olin Chemicals)solution containing 0.2 part of T-12 catalyst (dibutyl tin dilauratefrom Air Products) with stirring for at least two hours. The resultingpolyol-Lutonal M40 solution is then dried under vacuum in order toremove moisture. To this clear solution, 4.3 parts of N-3300multi-functional hexamethylene isocyanate prepolymers and 2.2 parts ofDESMODUR W, methylene bis(cyclohexyl-4-isocyanate), (both isocyanatesfrom Miles Inc.) are added at 60° C. in one portion. The reaction massis then casted onto a support film with desired thickness. Aftercompletion of the casting, the casted material is cured in an aircirculating oven at 100° C. for 60 minutes. After cooling to roomtemperature, a clear and pressure-sensitive adhesive slab is obtainedfor further testing on its physical properties.

EXAMPLE 2 Hydrophobic Polyurethane Adhesive With 23% Loading ofPolyvinyl Methyl Ether (Lutonal M40)

The same procedure as in Example 1 was used to prepare the 23% loadingsample except that the amount of each ingredient used in the preparationare changed to reflect the loading and NCO/OH ratio changes: 22.6 partsof Lutonal M40, 70.0 parts of Poly-G 26-37, 4.3 parts of N-3300, 2.9parts of DESMODUR W, and 0.2 part of T-12.

EXAMPLE 3 Hydrophobic Polyurethane Adhesive Without Polyvinyl MethylEther

A polyol solution is prepared by mixing 91.6 parts of hydrophobic polyol(Poly-G 26-37 from Olin Chemicals) and 0.2 part of T-12 catalyst at aroom temperature. The resulting clear solution is dried under vacuum. Tothis solution, 4.0 parts of N-3300 and 4.2 parts of DESMODUR W are addedin one portion at room temperature with stirring. After stirring for 10minutes at 60° C., the reaction mass is then casted and cured by usingthe same procedure specified in Example 1.

EXAMPLE 4 Hydrophilic Polyurethane Adhesive Without Polyvinyl MethylEther

The same procedure as in Example 3 is used to prepare a hydrophilicpolyurethane adhesive except that the hydrophobic polyol is substitutedwith a hydrophilic polyol Poly-G 55-37. The amount for each ingredientare as follows: 99.55 parts of Poly-G 55-37; 0.2 part of T-12 catalyst;3.38 parts of N-3300; 4.05 parts of DESMODUR W.

Properties of the Skin Barrier Materials

The samples from Examples 1 through 4 were tested as follow:

    __________________________________________________________________________              MVTR*                                                               Example                                                                            Lutonal                                                                            24-72 hrs                                                                          Water                                                                             Extractables                                               Number                                                                             M40 (%)                                                                            g/m.sup.2 /day                                                                     Uptake                                                                            24 hrs (%)                                                                         7 days (%)                                                                         Swelling                                                                           Disintegration                              __________________________________________________________________________    1    29   879  27  0.0  0.8  No   No                                          2    22   1278 10  0.0  0.6  No   No                                          3    0    2083 2   0.0  0.5  No   No                                          4    0    2170 285 2.5  --   Yes  No                                          __________________________________________________________________________     *Tested on 2 mil thick samples                                           

Water Vapor Transmission Test

ASTM Standard Test Methods of Water Vapor Transmission of MaterialsDesignation: E96-80 was used. The Water Method paragraph 3.2 of the testmethod was used.

In the Water Method, a dish is prepared containing distilled water andweighings are made to determine the rate of vapor movement through thespecimen from the water to a controlled atmosphere.

What is claimed is:
 1. A pressure-sensitive adhesive comprising apolyurethane polymer, resulting from a reaction of a polyisocyanate witha polyol, containing a dissolved water soluble polymer free frommoieties which will react with isocyanate groups.
 2. Thepressure-sensitive adhesive of claim 1 wherein said polymer has asolubility parameter in poorly hydrogen-binding solvents of from about 8to about
 10. 3. The pressure sensitive adhesive of claim 1 wherein saidwater soluble polymer is poly(vinylmethylether) orpoly(2-ethyl-2-oxazoline).
 4. The pressure-sensitive adhesive of claim 3wherein said water soluble polymer is poly(vinylmethylether).
 5. Thepressure-sensitive adhesive of claim 1 wherein said water solublepolymer is present in an amount of from about 1 to 40% by weight ofadhesive.
 6. The pressure-sensitive adhesive of claim 5 wherein saidwater soluble polymer is present in an amount of from about 25 to 35% byweight of the adhesive.
 7. The pressure-sensitive adhesive of claim 1wherein said polyurethane polymer has an excess hydoxyl functionality, aglass transition temperature of less than about 0° C., a moistureabsorption at equilibrium of at least about 20% of its weight, and apeel adhesion to human skin of between about 0.3 and 4 newtons/cm widthof the polymer.
 8. The pressure-sensitive adhesive of claim 7 whereinthe glass transition temperature is less than about -30° C., themoisture absorption at equilibrium is at least about 100% of its weight,and the peel adhesion is between about 0.5 and 3.5 newtons/cm width ofthe polymer.
 9. The pressure-sensitive adhesive of claim 1 wherein saidpolyurethane polymer has excess hydroxyl functionality, a glasstransition temperature of less than about 0° C., a moisture vaportransmission rate of at least about 300 grams/meter² /24 hours measuredat 37° C. and a 90% relative humidity gradient, and a peel adhesion tohuman skin of between about 0.5 and 3.5 newtons/cm width of the polymer.10. The pressure-sensitive adhesive of claim 9 wherein the glasstransition temperature of the polyurethane polymer is less than about-30° C., the moisture vapor transmission rate is at least about 500grams/meter² /24 hours, and the peel adhesion is between about 0.5 and3.5 newtons/cm width of the polymer.
 11. A pressure-sensitive adhesivecomprising a polyurethane polymer formed by first dissolving a watersoluble polyurethane polymer into a polyol component wherein said watersoluble polymer has a solubility constant in poorly hydrogen-bindingsolvents of from about 8 to 10 and being free from moieties reactivewith isocyanates; and the reaction of an isocyanate component and theso-formed polyol component at a molar ratio of isocyanate moieties tohydroxyl moieties of less than or equal to one with at least one of thecomponents having a functionality that is greater than two to facilitatecrosslinking, said polymer having a glass transition temperature of lessthan about 0° C., a moisture absorption at equilibrium of at least about20% of its weight, and a peel adhesion to human skin of between about0.3 and 4 newtons/cm width of the polymer.